1. Field of the Invention
The present invention relates to a tamping tool assembly for tamping ballast underneath two successive ties of a railroad track, which comprises two pairs of tamping tools succeeding each other in the direction of elongation of the railroad track, two of the tamping tools of the pairs being adjacent each other and the other two tamping tools of the pairs being remote from each other, vertically adjustable tamping tool carrier means, crank shaft means mounted on the tamping tool carrier means, drive means connecting the tamping tools to the crank shaft means for reciprocating the tamping tools in the direction of elongation of the railroad track, a drive for vertically adjusting the tamping tool carrier means for immersing the tamping tools in the ballast, and an independent drive for vertically adjusting one of the remote tamping tools for immersion in the ballast independently of the other tamping tools.
2. Description of the Prior Art
Such a ballast tamping tool assembly for simultaneously tamping ballast underneath two successive ties has been disclosed in Austrian patent No. 384,447. In this tamping tool assembly, a central crank shaft for vibrating the tamping tools is mounted on a vertically adjustable tamping tool carrier, and drives connect the two adjacent and the two remote tamping tools of two pairs of tamping tools to the central crank shaft. A parallelogram linkage connects each remote tamping tool to the tamping tool carrier for vertically adjusting each remote tamping tool in a vertical plane extending parallel to the direction of elongation of the railroad track independently of the vertical adjustment of the common tamping tool carrier.
U.S. Pat. No. 4,773,333 also describes a tamping tool assembly with a central crank shaft for vibrating the tamping tools which is mounted on a vertically adjustable tamping tool carrier, and drives connect the two adjacent and the two remote tamping tools of two pairs of tamping tools to the central crank shaft. The remote tamping tools have tamping picks which may be independently vertically adjusted.
In the ballast tamping tool assembly of published European patent application No. 314,933, four independently vertically adjustable tamping tools are arranged in succession for selectively immersing two or four tools in the ballast for tamping either a single tie or two successive ties.
U.S. Pat. No. 5,133,263 and Swiss patent No. 569,836 disclose tamping heads for simultaneously tamping three successive ties. The tamping tool assembly comprises two adjacently arranged, vertically adjustable tamping tool carriers each carrying three tamping tools, two of the tamping tools forming a central pair of tamping tools and being mounted on a respective one of the tamping tool carriers. The central one of the three successive ties can be tamped only when both tamping tool carriers are vertically adjusted to immerse the two tamping tools in the ballast adjacent the central tie.